Chlorine in mid-ocean ridge magmas: Evidence for assimilation of seawater-influenced components

Journal Article · Fri Dec 01 00:00:00 EST 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90094-X· OSTI ID:7061505

Michael, P J ^[1]; Schilling, J G ^[2]

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1. Univ. of Tulsa, OK (USA)
2. Univ. of Rhode Island, Kingston (USA)

Suites of depleted MORB glasses from the fast-spreading Pacific-Nazca Ridge at 28{degree}S and 32{degree}S and the slow-spreading eastern boundary of the Juan Fernandez microplate were analyzed for chlorine by electron microprobe. The Cl concentrations in FeTi basalts exceed by a factor of 5 to 10 the amounts that can be generated by fractional crystallization of the primitive magmas. Selective melting or breakdown of amphibole and incorporation of Cl-rich brine contained in the wall rocks may be important processes. A magmatic source for the additional Cl and H{sub 2}O cannot be ruled out on geochemical grounds but is physically unrealistic because it requires that large volumes of magma have crystallized and exsolved a Cl-rich vapor phase that has somehow migrated to a small magma chamber. Excess Cl in evolved magmas is best developed in evolved MORB from propagating or overlapping spreading centers such as the Galapagos Spreading Center at 85{degree}W and 95{degree}W and the west ridge of the Juan Fernandez microplate. Cl overenrichment has not been observed on slow-spreading ridges including the eastern ridge of the Juan Fernandez microplate, the Southwest Indian Ridge, and the mid-Atlantic Ridge. The assimilation of hydrothermally altered material could influence the concentration and isotopic ratios of other elements which have low abundances in MORB relative to seawater.

• OSTI ID: 7061505
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 53:12; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
BASALT
CHEMICAL COMPOSITION
PETROGENESIS
CHLORINE
CONCENTRATION RATIO
ELECTRON MICROPROBE ANALYSIS
GEOCHEMISTRY
MAGMA
MINERALIZATION
PACIFIC OCEAN
RIFT ZONES
SEAWATER
CHEMICAL ANALYSIS
CHEMISTRY
ELEMENTS
GEOLOGIC STRUCTURES
HALOGENS
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
MICROANALYSIS
NONMETALS
OXYGEN COMPOUNDS
ROCKS
SEAS
SURFACE WATERS
VOLCANIC ROCKS
WATER
580000* - Geosciences